This invention relates to continuous power systems. In particular, the present invention relates to continuous power systems that provide a continuous supply of electric power when a primary power supply fails, or when deterioration occurs in the power being supplied to the end user.
Continuous power systems are often used to insure that, in the event of a loss of power from a primary power supply, such as failure due to equipment malfunction, downed lines or other reasons, electric power continues to be supplied. This is particularly applicable in applications relating to, for example, telecommunication systems because such systems typically include facilities that may be in relatively isolated locations, such as a telecommunication repeater tower. Other applications of the present invention include hospital operating room equipment, computer systems, computerized manufacturing equipment, airplane radar guidance systems, etc. Continuous power systems typically are reliable systems that avoid equipment failures, costly downtime and equipment damage, as well as providing necessary power that otherwise would not be available.
Known continuous power systems may employ an uninterruptible power supply (UPS) to provide alternating current (AC) power to the end user or critical load. The AC power may be provided directly to the load, or it may be provided through known switching circuitry that also may be utilized to switch in back-up power when utility power fails.
For known continuous power systems, batteries or flywheels may be employed as energy storage subsystems to provide bridging energy while a fuel-burning engine is started. Such flywheel systems may include a flywheel connected to an electrical machine that can operate both as a motor and a generator. For example, U.S. Pat. No. 5,731,645 describes flywheel systems that provide backup power to the load in UPS systems. The electrical machine is powered by a DC buss to operate as a motor when acceptable power is received from the primary power supply. When power from the primary power supply fails (or is degraded), the electrical machine is rotated by the kinetic energy of the flywheel and operates as a generator to supply power to the DC buss.
Continuous power systems often use prime movers (e.g., fuel-burning engines) to drive backup generators during prolonged power outages. These prime movers, however, are often costly, complicated, and may require extensive ongoing maintenance. In addition, the engines themselves may fail to start, resulting in a loss of power to the critical load. Moreover, some localities limit the running time or the number of starts per year for backup generator engines, thereby limiting the ability to test and maintain such systems.
Other energy storage systems currently used to provide backup power are often expensive and complicated. For example, in typical battery energy storage systems, there is a risk that undetected battery damage or corrosion of battery terminals can result in a failure to deliver backup power when needed. Moreover, batteries have a limited shelf life, in addition to requiring expensive ventilation, drainage, air conditioning and frequent maintenance. Flywheel energy storage systems, while avoiding most of the disadvantages of batteries, can be expensive since they are often mechanically complex and can require complicated power electronics.
Some known systems provide long-term power by driving a shaft-mounted generator with a turbine. For example, U.S. Pat. No. 6,255,743 (application Ser. No. 09/318,728) describes an uninterruptible power supply system that includes a shaft-mounted generator and a turbine. These turbines may be open systems, where the turbine is driven by a fuel source that is regularly renewed, such as LP gas, methane, gasoline, diesel fuel. In such instances, the turbine exhaust is allowed to escape into the environment.
Other turbine systems, however, may be closed or partially-closed systems. In such systems, some or all of the turbine exhaust is recaptured by the system for later use. For instance, in a partially-closed system that is steam powered, the system may be configured to recapture the steam that is exhausted from the turbine. The system may then condense the steam (using a condenser or through natural cooling) into water prior to reheating, revaporizing and reusing the steam to drive the turbine.
An object of the present invention is to provide continuous power systems that are more reliable than conventional UPS systems.
Another object of the present invention is to provide continuous power systems that provide multiple sources of short-term backup energy.
A further object of the present invention is to provide continuous power systems in which a source of short-term backup energy is angular momentum.
A further object of the present invention is to provide continuous power systems in which a source of short-term backup energy is stored thermal energy.
A still further object of the present invention is to provide continuous power systems that include a closed-loop turbine system that operates at higher reliability than conventional systems.
The continuous power systems of the present invention provide backup power in the event of a loss of power or reduction in power quality from a primary power supplyxe2x80x94an OUTAGE. An OUTAGE, as defined herein, includes both an interruption in power from a source (such as utility power), as well as a degradation in quality of the power delivered by the source. This includes both short-termxe2x80x94in terms of seconds or minutes, and long-term, or extended OUTAGES (e.g., lasting hours, days, or even weeks).
Continuous power systems constructed in accordance with the present invention include a flywheel energy storage device that provides short-term backup power, as well as a source of stored thermal energy in the form of heated working fluid and other material (which may be referred to herein as a xe2x80x9cthermal storage devicexe2x80x9d). In addition, the continuous power systems of the present invention include a turbine that is driven by a closed-loop supply of working fluid to provide long-term backup power to the end user or critical load.
These continuous power systems may include an electrical machine that can operate as a motor or as a generator mounted to a shaft that also includes the flywheel energy storage device and the turbine. During STANDBY mode, power from the primary power supply drives the electrical machine as a motor, which rotates the shaft at a predetermined speed. The STANDBY speed of the shaft is selected so that the flywheel can store a given amount of kinetic energy as angular momentum that will be converted into electrical energy in the event of a loss or degradation of primary power. In addition, during STANDBY mode, an accumulator is provided with a supply of liquid that is heated to provide a second source of short-term backup power.
During SHORT-TERM OUTAGES, the flywheel drives the electrical machine as a generator to provide the necessary backup power. As the length of time of the OUTAGE continues and the stored kinetic energy is depleted, the flywheel slows down. Once a predetermined speed is reached, the continuous power system activates its second source of short-term backup powerxe2x80x94the thermal source. The stored heated fluid in the accumulator is provided to a preheater/evaporator device that adds enthalpy to the fluid that is provided to the turbine. The fluid is evaporated in this process, and the vapor drives the turbine. The turbine then drives the shaft, thereby enabling the electrical machine to continue to operate as a generator that supplies backup energy to the end user or critical load.
If it appears that the OUTAGE is going to be EXTENDED, based on a predetermined factor such as, for example, a reduced level of stored thermal fluid in the accumulator, a gas-fired burner is started, and the system enters EXTENDED OUTAGE mode. In this mode, the working fluid used to power the turbine is cycled via a closed loop through the preheater/evaporator to the turbine. Exhaust vapor is recaptured, condensed and resupplied to the preheater/evaporator. Those familiar with the art will appreciate that this process is commonly known as the Rankine cycle. A further feature of the closed-loop aspect of the present invention is the use of the condensed working fluid as a lubricant for the bearings of the shaft-mounted components, such as the flywheel, turbine and electrical machine. This eliminates the need for rotating seals and allows the entire system to be hermetically sealed.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.